is it true that scientists can turn parts of brains on and off ?if so would they be able to get into the brain cells

Question: is it true that scientists can turn parts of brains on and off ?if so would they be able to get into the brain cells then tweak the DNA so that it stops or gets smaller?
- Keywords:
  brain,
  DNA,
  switch
Asked by Bombdat to Carolyn, Peter, Richard, Sara on 19 Nov 2015.
- Sara Falcone answered on 19 Nov 2015:
  
  Hello Bombdat 🙂
  
  It is possible to switch off cells of the brain, yes. You do it stopping the mechanism that creates-propagates the electric impulse.
  You can even target just few cells using a technique called “optogenetics”, I am not sure though what you’d like to get smaller?

Question: is it true that scientists can turn parts of brains on and off ?if so would they be able to get into the brain cells then tweak the DNA so that it stops or gets smaller?